Emetophobia is an excessive or irrational fear of vomiting or of being around others who are vomiting. It is one of the most common specific phobias. In survey research, six percent of the U.S. population claims to fear being sick, although a much smaller number suffer from actual emetophobia, which manifests itself through a variety of phobic behavior.

It is unknown what exactly causes Emetophobia to develop, but the accepted theory says that Emetophobia can be the result of a traumatic incident of vomiting between the ages of six and ten. Most emetophobics claim they can will themselves to avoid vomiting, and a survey of an Internet group of emetophobics found that the average member had last vomited at least twelve years earlier. On average, it is suggested that most emetophobics have been sick five or fewer times in their lives.

Emetophobics are known to go to great lengths to avoid people who may be sick or where a threat of infection is perceived. Some Emetophobics will avoid being in public places where they fear people may vomit or where they think there may be a higher probability of someone vomiting (such as a bar or a nightclub). Many emetophobics would rather endure prolonged nausea than face the fear of vomiting; in fact, emetophobes can tolerate nausea for more than twenty hours, while the average person would vomit to relieve nausea after an average of twenty minutes.